Epoxy resin composition and laminate using the same

ABSTRACT

The present invention relates to a nonflammable epoxy resin composition for using a thin copper film laminate, which is applied to a printed circuit board (PCB), and using the same. The present invention provides for nonflammable epoxy resin composition for using a thin copper film laminate, comprising bisphenol A-type epoxy resin, multifunctional epoxy resin, an imidazole-based curing catalyst, and a curing retarder, and using the same. As described above, since the ring-open of the epoxy group is prompted by an imidazole catalyst, without the use of dicyandiamide, epoxy polymer reaction occurs due to the chain-reaction of epoxy group, and the glass-transition temperature is 170° C. or greater, the nonflammable epoxy resin composition for using a thin copper film of the present invention has a strong heat-resistance, lower dielectric constant, controllable gelation time, and does not require the use of non-harmful catalysts to the human body.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on application No. 2000-0031965 filed with theKorean Industrial Property Office on Jun. 10, 2000, the content of whichis incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to an epoxy resin composition for using anonflammable thin copper film laminate, which is applied to a printedcircuit board (PCB), and a laminate using the same.

(b) Description of the Related Art

In conventional epoxy resin composition, an amine-based curing agent anda curing prompter have been generally used as well as brominateddifunctional and multifunctional epoxy resins as the main material. Thebrominated epoxy resin has been used to bring non-flammability, andtrifunctional or multifunctional epoxy resin has been also used toincrease heat-resistance and mechanical strength. However, since thecure reaction does not occur easily with the use of only epoxy resin,the epoxy resin may be cured by adding a curing agent into the epoxyresin, and activating the epoxy group.

At present, dicyandiamide has been generally used as a curing agent,however imidazole is generally added as a curing catalyst, since thereaction rate of dicyandiamide with epoxy resin is very slow, in thecase where the dicyandiamide is only used. U.S. Pat. Nos. 5,308,895,5,508,328, 5,620,789, and 5,721,323 show that boric acid is added as acure retarder in order to increase a glass-transition temperature, bycontrolling a curing rate and increasing a curing degree due to increaseto a curing density. However, dicyandiamide is used as a curing agent,and the glass-transition temperature (Tg) is between 140° C. and 160° C.

Since a coordinate bond with the boric acid and the imidazole at lowtemperatures prevents the imidazole from curing the epoxy resin, theepoxy resin has an improved stability at room temperature, and thecoordinate bond inhibits curing the epoxy resin at low temperatures. Ingeneral, the boric acid and imidazole decompose with each other at 120°C. or greater, the decomposing imidazole improves the reactivity ofdicyandiamide, and a ring-open of epoxy group is prompted due to theincrease in reactivity. As a result, the curing rate of the epoxy resinincreases, and then the glass-transition temperature increases.

However, the use of dicyandiamide requires organic solvents such asdimethylformamide (DMF), and N-methyl 2-pyrrolidone, which are harmfulto the human body, due to the solubility of dicyandiamide, and alsorequires stable storage, since the dicyandiamide deposits at lowtemperatures. As well, heat-resistance of the epoxy resin and thedicyandiamide is limited at 250° C. or above, since the dicyandiamide ispyrolyzed by itself at 200° C. or above. In addition, there is anincrease in the dielectric constant of the epoxy resin, that resultsfrom adding dicyandiamide.

Accordingly, in the case where imidazole prompts the ring-open of theepoxy resin without the use of dicyandiamide, and epoxy polymer reactionoccurs through the chain-reaction of the epoxy group, a thin copper filmlaminate that has a glass-transition temperature in the range of 170° C.or greater and improved heat-resistance may be fabricated, since thepolymer bond gets to be strong, the curing density can increase. Inaddition, the thin copper film laminate has decreased dielectricconstant than the conventional one. However, the epoxy resin compositionfor the thin copper film laminate, as mentioned above, has not appeared.

The heat-resistance of nonflammable epoxy resin for using thin copperfilm laminate is represented by the glass-transition temperature, andthe epoxy resin having a glass-transition temperature in the range of120° C. to 150° C. has been generally used as a FR-4 product. As theglass-transition temperature is higher, the epoxy resin has a betterheat-resistance due to the high curing density of epoxy resin, asuitable size at high temperatures due to small heat expansion, lowerabsorbability to water due to dense molecular structure. Therefore, athin copper film laminate may be manufactured, compared to a polymerresin having low glass-transition temperature. In order to increase theglass-transition temperature, certain methods have been applied whereepoxy resin having a trifunctional group or a multifunctional group isadded, novolac epoxy is added, and BT resin or polyimide is blended.

SUMMARY OF THE INVENTION

The present invention is made in consideration of the problems of theprior art, and it is an object of the present invention to provide anonflammable epoxy resin composition for a thin copper film laminate,having an improved heat-resistance due to the increase to aglass-transition temperature of 170° C. or greater, which results froman epoxy polymer reaction that is prompted to a ring-open of epoxy groupby imidazole without use of dicyandiamide.

It is another object to provide the nonflammable epoxy resin compositionfor a copper thin film laminate, having low dielectric constant, and alaminate using the same.

It is another object to provide the nonflammable epoxy resin compositionfor a copper film laminate, that is prepared without use of a harmfulsolvent to human body, and a laminate using the same.

It is another object to provide the nonflammable epoxy resin compositionhaving a controllable gelation time through controlling a curing rate ofepoxy resin and a laminate using the same.

In order to achieve these objects, the present invention provides anonflammable epoxy resin composition for using a thin copper filmlaminate comprising:

a) brominated bis-phenol A-type difunctional epoxy resin;

b) multifunctional epoxy resin;

c) an imidazole-based curing catalyst; and

d) a curing retarder.

The present invention also provides a thin copper film laminate, thatcomprises a fiber glass laminate impregnated with one or more epoxyresins, and the thin copper film located on the outer of the fiber glasslaminate, wherein the fiber glass laminate and the thin copper film areunited with each other.

DETAILED DESCRIPTION OF THE PREFERRED INVENTION

In the following detailed description, only the preferred embodiment ofthe invention has been shown and described, simply by way ofillustration of the best mode contemplated by the inventors of carryingout the invention. As will be realized, the invention is capable ofmodification in various obvious respects, all without departing from theinvention. Accordingly, the description is to be regarded asillustrative in nature, and not restrictive.

The epoxy resin composition of the present invention, which is used fora thin copper film laminate of a nonflammable impregnated fiber glasslaminate, is cured by imidazole catalyst, due to a ring-open of epoxygroup, instead of the conventional dicyandiamide.

The bis-phenol A-type epoxy resin of the present invention comprisesbromine, that is preferably from 15 wt % to 55 wt %, and the brominebrings non-flammability into a thin copper film laminate, and theequivalent ratio of epoxy group is preferably from 300 to 1500.

In addition, the multifunctional epoxy resin of the present inventionhas three or more epoxy functional groups per molecule, that istrifunctional, and tetrafunctional and novolac resin as a generalmultifunctional epoxy resin. In general, as the functional groupsincrease, the epoxy resin has greater glass-transition temperature.

The epoxy resin needs a curing agent in curing process, and anamine-based curing agent has been used as a conventional curing agent,that has a problem on solubility to an organic solvent, and requiressophisticated processes. Accordingly, as supplement to the conventionalcuring agent, the curing agent of the present invention includesimidazoles, such as 1-methyl imidazole, 2-methyl imidazole, 2-ethyl4-methyl imidazole, 2-phenyl imidazole, 2-cyclohexyl 4-methyl imidazole,4-butyl 5-ethyl imidazole, 2-methyl 5-ethyl imidazole, 2-octhyl 4-hexylimidazole, 2,5-choloro-4-ehtyl imidazole, and 2-butoxy 4-allylimidazole, and imidazole derivatives.

The content of the imidazoles is preferably based on 0.1 to 20 weightpart, compared to 100 weight part of epoxy resin (the total weight ofdifunctional epoxy resin and multifunctional epoxy resin), and morepreferably based on 1 to 5 weight part.

The use of imidazoles increases the gelation rate of epoxy resin, andepoxy resin is uneasy to mold, since the gelation time is shorter to 200seconds or less. Therefore, a curing retarder is used in order tocontrol the gelation rate, and increase the gelation time to 200 secondsor more, and the curing retarder brings convenience to mold. The curingretarder includes boric acid, salicylic acid, hydrochloric acid,sulfuric acid, oxalic acid, terephthalic acid, isophthalic acid,phosphoric acid, lactic acid, phenyboric acid, and toluene sulfuricacid, and the amount of the curing retarder used is preferably from 0.1to 10 equivalent weight per mole based on equivalent weight per mole ofimidazole, more preferably from 0.5 to 5 equivalent weight per mole ofimidazole.

Though the epoxy resin of the present invention may be used withmultifunctional epoxy resin in small amounts, the present invention hasglass-transition temperature in the range of 170° C. or greater, sincethe curing rate and curing density of epoxy resin are controlled byadding the imidazole, respectively as a catalyst, and a curing retarder.Therefore, it can manufacture nonflammable thin copper film laminatehaving strong heat-resistance. In addition, the use of imidazole may notneed the use of an amine-based curing agent such as dicyandiamide, whichhas a low solubility to an organic solvent, and an undesirable propertyat high temperatures, and also may not need the use of a harmful solventto the human body such as DMF on the curing process. Therefore, theprocess may be environmentally desirable, and the dielectric constantmay decrease.

While the present invention has been described in detail with referenceto the preferred embodiments, those skilled in the art will appreciatethat various modifications and substitutions can be made thereto withoutdeparting from the spirit and scope of the present invention as setforth in the appended claims.

EXAMPLES Example 1

(Preparation for Epoxy Resin Composition)

According to the composition shown in Table 1, an epoxy resincomposition was prepared.

At first, 2.0 g of 2-phenyl imidazole and 0.85 g of boric acid wereadded into 500 ml beaker, and then the mixture was completely dissolvedafter adding 25 g of methylcellosolve (MCS: ethylene glycol monomethylether) thereinto.

After 125 g of a brominated bis-phenol A-type epoxy resin (prepared byLG Chem, LER-1222M80) as a difunctional epoxy resin of which equivalentweight is 450, was added into the solution, the solution was stirreduntil completely mixed.

In addition, 50 g of tetrafunctional epoxy resin (manufactured by ShellCorp., EPON 1030), which was completely dissolved in 50 g of MCS, wasadded the solution, and then was stirred until completely mixed.

The gelation time of the epoxy resin composition was measured by a hotplate having the temperature of 170° C., the gelation time was 210seconds.

(Manufacture of Thin Copper Film Laminate)

The prepared epoxy resin composition was impregnated with fiberglass(fabricated by Nittobo Corp., product No.7628), and fiberglass prepreg,of which the content of epoxy resin is 43 wt %, was prepared byhot-air-drying.

After 8 sheets of the fiberglass prepreg was laminated, 35 μm of copperfilms were further laminated on and below the prepreg, and the laminatedfilms were heated and pressed for 90 minutes at 185° C. under 40 kg/cm¹,then 1.6 mm of copper film laminate in thickness was finally prepared.

(Test for Thin Copper Film Laminate)

The thin copper film was removed from thin copper film laminate byetching, and glass-transition temperature of the film was 177° C. bymeasuring with DSC (differential scanning calorimeter).

Lead-resistance was measured by placing a sample that was cut with thesize of 5 cm by 5 cm and the thickness of 1.6 mm under a lead-furnace,and measuring the bearing time of the sample.

Heat-resistance in an oven was measured by placing a sample that was cutwith the size of 5 cm by 5 cm and the thickness of 1.6 mm under an ovenhaving constant temperature of 270° C., and measuring the bearing timeof the sample.

In order to verify change of dielectric constant of a product removeddicyandiamide, a thin copper film laminate was manufactured in the sameway as described above, fiber glass was changed into product No. 2116,and a product having 0.5 mm in thickness was manufactured, finally thedielectric constant of the product was measured according to JIS C 6481.The results are shown in Table 1.

Comparative Example 1

(Preparation for Epoxy Resin Composition with Use of Dicyandiamide)

An epoxy resin composition was prepared with use of dicyandiamide as acuring agent, which was generally used for preparing FR-4, according tothe composition shown in Table 1.

2.0 g of 2-phenyl imidazole and 5.60 g of dicyandiamide were added in500 ml beaker, and then the mixture was completely dissolved afteradding 45 g of methylcellosolve (MCS: ethylene glycol monomethyl ether)and 10 g of DMF thereinto.

After 125 g of a brominated bis-phenol A-type epoxy resin (prepared byLG Chem, LER-1222M80) as a difunctional epoxy resin of which equivalentweight is 450, was added into the solution, the solution was stirreduntil completely mixed.

In addition, 50 g of tetrafunctional epoxy resin (manufactured by ShellCorp., EPON 1030), which was completely dissolved in 50 g of MCS, wasadded to the solution, and then was stirred until completely mixed.

The gelation time of the epoxy resin composition was measured by a hotplate having the temperature of 170° C., the gelation time was 250seconds.

In the same way according to Example 1.6 mm copper film laminate inthickness was manufactured, and glass transition temperature,lead-resistance, and heat-resistance in an oven of the thin copper filmlaminate was also measured.

In addition, in the same way according to Example 1, 0.5 mm product inthickness was manufactured and dielectric constant was measured. Thetest results are shown in Table 1.

Comparative Example 2 and 3

In the same way according to Example 1, glass-transition temperature,lead-resistance, and heat-resistance in an oven of conventional FR-4 andFR-5 were measured, and the test results are shown in Table 1.

TABLE 1 Comparative Comparative Comparative Example 2 Example 3 KindExample 1 Example 1 (FR-4) (FR-5) Epoxy Resin Difunctional 125 125 — —Composition Epoxy Resin (phr) (LER1222M80) Tetrafunctional 50 50 EpoxyResin (EPON-1030) Imidazoles 2.0 0.2 (2-phenyl imidazole) Dicyandiamide— 5.60 Curing retarder 0.85 — (boric acid) Properties Gelation time 210250 — — (sec) Glass-transition 177 158 125 175 temperature (° C.) Leadresistance 900 or longer 305 300 618 (sec) Heat-resistance 1200 or 605585 715 in an oven (sec) longer Dielectric 4.4˜4.5 4.7˜4.8 — — constant

Example 2˜5

As shown in Table 2 below, the contents of imidazole and curing retarderwere changed, and in the same way according to the above Example 1,epoxy resin composition was prepared and a thin copper film laminate wasmanufactured. The properties are shown in Table 2.

TABLE 2 Exam- Exam- Exam- Exam- Kind ple 2 ple 3 ple 4 ple 5 Epoxy ResinDifunctional 125 125 125 125 Composition epoxsy resin (phr) (LER1222M80)Tetrafunctional 50 50 50 50 Epoxy resin (EPON-1031) Imidazoles 1.0 1.52.0 2.5 (2-phenyl imidazole) Curing retarder 0.44 0.64 0.85 1.05 (boricacid) Properties Gelation time 366 230 210 149 (sec) Glass-transition164 172 180 185 temperature (° C.)

According to the test results, as the content of imidazole increases,gelation time decreases due to the increase of the gelation time of theepoxy resin, however, after mold, the glass-transition temperature ofthe thin copper film laminate increases due to the increase in thecuring density.

Example 6˜9

As shown in Table 3 below, the content of imidazole was changed, and inthe same way according to the above Example 1, epoxy resin compositionwas prepared, and a thin copper film laminate was manufactured. Theproperties are shown in Table 3.

TABLE 3 Exam- Exam- Exam- Exam- Kind ple 6 ple 7 ple 8 ple 9 Epoxy ResinDifunctional 125 125 125 125 Composition epoxy resin (phr) (LER1222M80)Tetrafunctional 50 50 50 50 Epoxy resin (EPON-1031) Imidazoles 2.0 2.02.0 2.0 (2-phenyl imidazole) Curing 0.64 0.83 1.09 1.30 retarder (boricacid) Properties Gelation time 230 250 250 205 (sec) Glass-transition172 175 176 173 temperature (° C.)

The desired gelation time was measured by controlling the content ofimidazole and boric acid, respectively used as a curing agent and acuring retarder, and the glass-transition temperature increased to 170°C. or greater.

As described above, since the ring-open of the epoxy group is promptedby an imidazole catalyst, without use of dicyandiamide, epoxy polymerreaction occurs due to the chain-reaction of epoxy group, and theglass-transition temperature is 170° C. or greater, the nonflammableepoxy resin composition for using a thin copper film laminate of thepresent invention has a strong heat-resistance, lower dielectricconstant, controllable gelation time, and does not require the use ofnon-harmful catalysts to the human body.

What is claimed is:
 1. A nonflammable epoxy resin composition for a thincopper film laminate, which comprises: a) brominated bis-phenol A-typedifunctional epoxy resin; b) multifunctional epoxy resin; c) animidazole-based catalyst; and d) a curing retarder, wherein thecomposition is substantially free of dicyandiamide, and has a glasstransition temperature of 170° C. or more.
 2. The epoxy resincomposition according to claim 1, wherein the difunctional epoxy resinof a) has bromine of which content is from 15 to 55 wt %.
 3. The epoxyresin composition according to claim 1, wherein the multifunctionalepoxy resin of b) selected from a group of epoxy resin consisting oftrifunctional epoxy, tetrafunctional epoxy, novolac resin and a mixturethereof.
 4. The epoxy resin composition according to claim 1, whereinthe imidazole catalyst for a curing reaction of c) selected from a groupconsisting of 1-methyl imidazole, 2-methyl imidazole, 2-ethyl 4-methylimidazole, 2-phenyl imidazole, 2-dyclohexyl 4-methyl imidazole, 4-butyl5-ethyl imidazole, 2-methyl 5-ethyl imidazole, 2-octyl 4-hexylimidazole, 2,5-choloro-4ehtyl imidazole, 2-butoxy 4-allyl imidazole, anda mixture thereof.
 5. The epoxy resin composition according to claim 1,wherein the content of the imidazole catalyst of c) is based on 0.1 to20 weight part, compared to epoxy resin based on 100 weight part.
 6. Theepoxy resin composition according to claim 1, wherein the curingretarder of d) selected from a group consisting of boric acid, salicylicacid, hydrochloric acid, sulfuric acid, oxalic acid, terephthalic acid,isophthalic acid, phosphoric acid, lactic acid, phenyboric acid, toluenesulfuric acid, and mixture thereof.
 7. The epoxy resin compositionaccording to claim 1, wherein the content of the curing retarder of d)is from 0.1 to 10 equivalent weight, compared to the equivalent weightof imidazole catalyst.
 8. A thin copper film laminate, which comprises afiber glass laminate impregnated with one or more epoxy resincompositions, and a copper film located on the outside of the glassfiber laminate, wherein the fiber glass laminate and the copper film isunited with each other through heating and pressing, wherein the epoxyresin composition comprises: a) brominated bis-phenol A-typedifunctional epoxy resin; b) multifunctional epoxy resin; c) animidazole-based catalyst; and d) a curing retarder, and it issubstantially free of dicyandiamide, and has a glass transitiontemperature of 170° C. or more.